Glyphosate, the main ingredient in a number of commercial herbicides, is beginning to lose its effectiveness in soybean, corn and cotton crops.

Written by

A much-used herbicide, which for years has helped farmers throughout the United States increase profits, is losing its effectiveness and forcing producers to spend more and use more chemicals to control the weeds that threaten yields.

"I've gone from budgeting $45 an acre just two years ago to spending more than $100 an acre now to control weeds," said Mississippi farmer John McKee, who grows corn, cotton and soybeans on his 3,300-acre farm in the Delta.

The problem is Roundup, a herbicide introduced in the 1970s, and its partner, Roundup Ready crop seeds, genetically modified to withstand ...